A conventional power supply device will be described below with reference to FIGS. 7A and 7B. In the arrangement disclosed in PTL 1, for example, as shown in FIG. 7A, a substrate holder 601 of a power supply device is held to be rotatable inside a vacuum vessel 630. The substrate holder 601 has a slidable surface using surface contact about a rotation axis C of a rotation column 602 as its center between the rotation column 602 and a base 603 which supports the load of the rotation column of the substrate holder 601. A rotary joint made of a plurality of conductive annular members 604 arranged concentrically is arranged to make it possible to stably supply the power to the electrode of the electrostatic chuck without causing unstable rotation of the substrate holder 601. As for a bipolar electrostatic chuck for supplying power to a plurality of electrodes, a plurality of rotary joints are aligned in the rotation axis direction to sandwich insulating members 605a and 605b between the adjacent rotary joints, thereby maintaining the insulating state between the plurality of electrodes.
To obtain a stable rotation operation in this structure, the insulating members 605a and 605b are arranged on the side of the rotation column 602 of the substrate holder 601 and on the side of the base 603 which supports the load of the rotation column and the like. A minimum gap 607 must be formed between the insulating members. The rotary joint has an incomplete sealing property, and a very small amount of liquid may leak from the rotary joint. A drain port is generally formed to drain the leaking liquid outside